In recent years, the mainstream of image-recording materials has been materials for forming color images in particular. More specifically, recording materials based on inkjet recording, recording materials based on heat-sensitive image transfer, recording materials based on electronic photography, silver halide photosensitive materials based on transfer, printing inks, recording pens, and the like have been widely utilized. Moreover, in image pickup devices such as CCD in picture-taking instruments and in LCD and PDP as displays, color filters are employed for recording and reproducing color images.
In these color image recording materials and color filters, coloring matter (dyes or pigments) of three primary colors for so-called additive color mixing or subtractive color mixing are employed for reproducing or recording full-color images. However, there actually exists no coloring matter which has absorption properties capable of realizing a preferable color reproduction range and which is fast enough to endure various use conditions and environmental conditions, so that improvement is strongly desired.
Because of inexpensive material costs, capability of high-speed recording, reduced noise in recording operations, and ease in color recording, inkjet recording has rapidly come into wide use and is still making further progress.
Inkjet recording methods include a continuous method in which liquid droplets are jetted continuously and a on-demand method in which liquid droplets are jetted depending on signals of image information, and ejection methods thereof include a method in which liquid droplets, pressed by a piezoelectric element, are ejected, a method in which liquid droplets are ejected by bubbles generated in the ink by heat, a method in which ultrasonic waves are used, and a method in which liquid droplets are suction-ejected by electrostatic force.
Moreover, as an inkjet recording ink composition, aqueous ink, oil-based ink, and solid (fusion-type) ink are used.
The properties required for the coloring matter in such an inkjet recording ink composition are satisfactory solubility or dispersibility in a solvent, capability of high-density recording, excellent hue, fastness to light, heat, and active gases (oxidizing gases such as NOx and ozone, SOx, etc.) in the environment, excellent fastness to water and chemicals, excellent fixation and little bleeding on image-receiving materials, excellent storability as ink, freedom from toxicity, high purity, and availability at a low cost.
However, it is extremely difficult to obtain coloring matter that highly satisfies these requirements. In particular, there is a strong demand for coloring matter that has a satisfactory hue and exhibits fastness to light, humidity, and heat, and particularly, when printing is carried out on an image-receiving material having an ink-receiving layer containing porous white inorganic pigment particles, it is strongly desired that the coloring matter exhibits fastness to oxidizing gases such as ozone in the environment.
Heretofore, as a coupling component for azo dyes, phenol, naphthol, aniline, and the like have been widely used. As azo dyes obtainable from these coupling components, dyes disclosed in EP0761771, Japanese Patent No. 2716541, and so forth are known, for example, but these dyes have a problem of inferior lightfastness.
Moreover, any dyes known in the conventional art exhibit extremely insufficient fastness to oxidizing gases such as ozone.
The present inventors have investigated to develop a dye exhibiting fastness to oxidizing gases such as ozone and have conceived to use a nitrogen-containing heterocyclic compound as the coupling component departing from the conventional coupling components such as phenol, naphthol, and aniline. Heretofore, azo dyes using pyridine or pyrazine as the coupling component have been described, for example, in German Patent No. 2743097. However, the use of these dyes for inkjet recording ink was not known at that time. This is because these dyes are all oil-soluble and it is difficult to synthesize water-soluble counterparts of these dyes. Therefore, it was impossible to synthesize water-soluble counterparts of these dyes and to employ ink containing such dyes for image formation such as inkjet recording.
The invention aims at solving the above problem in the conventional art and achieving the following object.
Namely, it is an object of the invention to provide:    (1) various coloring compositions such as a printing ink composition (e.g., inkjet recording ink) which afford colored images and colored materials excellent in water resistance and fastness using a novel azo compound having an excellent water resistance and a sufficient fastness to light, heat, humidity, and active gases in the environment as a black dye, and    (2) an inkjet recording ink composition and an inkjet recording method capable of forming images having an excellent water resistance and a high fastness to light and active gases in the environment, particularly ozone gas.